On Sat, Dec 14, 2013 at 08:30:06AM +1100, Dave Chinner wrote:
> > if (atomic_dec_and_test(&dqp->q_nrefs)) {
> > if (list_lru_add(&mp->m_quotainfo->qi_lru, &dqp->q_lru))
> > XFS_STATS_INC(xs_qm_dquot_unused);
> > }
> >
> > given that the only locking we need is the internal lru lock?
>
> Yes, I think it is.
>
> However, that involves changing all the callers of dqput to not hold
> the dqlock when they call, which is a bigger change than was
> necessary to avoid the lock contention problem. i.e. it doesn't seem
> to be in a fast path that needed immediate fixing, so I didn't touch
> it.
Given that the lru list lock nests inside dqlock we can just turn
dqput into:
void
xfs_qm_dqput(
struct xfs_dquot *dqp)
{
ASSERT(dqp->q_nrefs > 0);
ASSERT(XFS_DQ_IS_LOCKED(dqp));
trace_xfs_dqput(dqp);
xfs_qm_dqrele(dqp);
xfs_dqunlock(dqp);
}
But with my other patch we can probably replace most callers
with xfs_qm_dqrele, and the remaining ones with an opencoded
version that first drops the lock easily.
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